HBASE-18480 The cost of BaseLoadBalancer.cluster is changed even if the rollback is done

Author: chia7712

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/BaseLoadBalancer.java

@@ -805,6 +805,7 @@ void regionMoved(int region, int oldServer, int newServer) {
       } else if (oldServer >= 0 && (numRegionsPerServerPerTable[oldServer][tableIndex] + 1)
           == numMaxRegionsPerTable[tableIndex]) {
         //recompute maxRegionsPerTable since the previous value was coming from the old server
+        numMaxRegionsPerTable[tableIndex] = 0;
         for (int serverIndex = 0 ; serverIndex < numRegionsPerServerPerTable.length; serverIndex++) {
           if (numRegionsPerServerPerTable[serverIndex][tableIndex] > numMaxRegionsPerTable[tableIndex]) {
             numMaxRegionsPerTable[tableIndex] = numRegionsPerServerPerTable[serverIndex][tableIndex];

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java

@@ -17,6 +17,7 @@
  */
 package org.apache.hadoop.hbase.master.balancer;
 
+import com.google.common.annotations.VisibleForTesting;
 import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -318,6 +319,12 @@ public synchronized List<RegionPlan> balanceCluster(TableName tableName, Map<Ser
     return balanceCluster(clusterState);
   }
 
+  @VisibleForTesting
+  Cluster.Action nextAction(Cluster cluster) {
+    return candidateGenerators.get(RANDOM.nextInt(candidateGenerators.size()))
+            .generate(cluster);
+  }
+
   /**
    * Given the cluster state this will try and approach an optimal balance. This
    * should always approach the optimal state given enough steps.
@@ -384,9 +391,7 @@ public synchronized List<RegionPlan> balanceCluster(Map<ServerName,
     long step;
 
     for (step = 0; step < computedMaxSteps; step++) {
-      int generatorIdx = RANDOM.nextInt(candidateGenerators.size());
-      CandidateGenerator p = candidateGenerators.get(generatorIdx);
-      Cluster.Action action = p.generate(cluster);
+      Cluster.Action action = nextAction(cluster);
 
       if (action.type == Type.NULL) {
         continue;

hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticLoadBalancer.java

@@ -280,6 +280,27 @@ public void testSkewCost() {
     assertEquals(1, costFunction.cost(), 0.01);
   }
 
+  @Test
+  public void testCostAfterUndoAction() {
+    final int runs = 10;
+    loadBalancer.setConf(conf);
+    for (int[] mockCluster : clusterStateMocks) {
+      BaseLoadBalancer.Cluster cluster = mockCluster(mockCluster);
+      loadBalancer.initCosts(cluster);
+      for (int i = 0; i != runs; ++i) {
+        final double expectedCost = loadBalancer.computeCost(cluster, Double.MAX_VALUE);
+        Cluster.Action action = loadBalancer.nextAction(cluster);
+        cluster.doAction(action);
+        loadBalancer.updateCostsWithAction(cluster, action);
+        Cluster.Action undoAction = action.undoAction();
+        cluster.doAction(undoAction);
+        loadBalancer.updateCostsWithAction(cluster, undoAction);
+        final double actualCost = loadBalancer.computeCost(cluster, Double.MAX_VALUE);
+        assertEquals(expectedCost, actualCost, 0);
+      }
+    }
+  }
+
   @Test
   public void testTableSkewCost() {
     Configuration conf = HBaseConfiguration.create();